1. Field of the Invention
The present invention relates to a method and device for data decryption, a method and device for device identification, a recording medium, a method of disk production, and a method and apparatus for disk recording, and particularly to a method and device for data decryption, a method and device for device identification, a recording medium, a method of disk production, and a method and apparatus for disk recording which are all intended to decrypt encrypted data protectively.
2. Description of Related Art
Recently, the format of digital video disk (will be termed "DVD" hereinafter) is going to be standardized, and DVDs are expected to take the place of conventional analog video disks. With the intention for long-time recording, video data is recorded on a DVD by being rendered the compressed encoding, e.g., based on the MPEG (Moving Picture Expert Group) scheme that will be dealt with exclusively in the following explanation. Accordingly, a record of data needs to be decoded at the time of playback.
It becomes possible, by the way, for a DVD owing to the digital recording of video data to produce its copies on other recording mediums at virtually the same output quality as the original DVD. Namely, there is a possibility of such an illegal conduct as manufacturing a stamper by leading video data out of the data path between the disk driver and MPEG decoder and producing illegitimate copy disks in large scale from it. Another possibility is manufacturing a stamper by decoding video data reproduced by the disk driver with an imitated MPEG decoder and producing illegitimate copy disks in large scale from it.
As a conceivable manner of precluding the illegal copy of DVDs and the use of imitated MPEG decoders, video data reproduced by the disk driver is encrypted based on an encryption key and fed to the MPEG decoder upon judging the legitimacy of the MPEG decoder. The MPEG decoder decrypts the encrypted video data by using the encryption key and thereafter decodes the encoded video data.
Based on this counter measure against the illegal conduct, video data reproduced by the disk driver is not fed to the MPEG decoder unless it is a legitimate device, whereby the illegal copy of DVDs and the use of imitated MPEG decoders can be precluded. Even if the disk driver is accessed with an imitated MPEG decoder and reproduced video data is led out, the encrypted data cannot be used intact, and accordingly DVDs are protected from being copied practically.
However, the conventional scheme of encryption of video data based on a simple encryption key before it is fed to the MPEG decoder by which reproduced and encrypted video data is decrypted is susceptible to breaking of encryption key.